1. Field of the Invention
The invention relates to an automatic gain control (AGC) circuit comprising a digitally-controlled amplifier having a gain control loop including a level detector, a threshold circuit and a digital gain control signal generator coupled to a gain control input of the digitally controlled amplifier for supplying thereto, a digital gain control signal, as well as to a digital audio broadcast (DAB) receiver comprising such an AGC circuit.
2. Description of the Related Art
An AGC circuit of this kind is known, e.g., from U.S. Pat. No. 4,774,474. The known AGC provides for an automatic digital, gain setting of the digitally-controlled amplifier, such that the output signal is stabilized at a particular predetermined level. The digitally-controlled amplifier may comprise a number of gain stages in series and/or parallel, which can be switched off and on, depending on the gain setting required to stabilize the output signal level. Each gain stage can be optimized for linearity, signal-to-noise ratio and gain within its working area. This allows optimization of the digitally-controlled amplifier at small input signal amplitudes for proper signal-to-noise ratio at high gain factor. The digitally-controlled amplifier can be optimized at large input signal amplitudes for accurate linearity and low gain factor.
However, small deviations around the switching levels of the known digital gain control signal give rise to repeated switching between two gain settings. This modulates the output signal of the digitally-controlled amplifier, thereby causing an increase in the bit error rate, which may cause, e.g., audible distortions to occur.